System and Method for Aircraft Braking System Usage Monitoring

ABSTRACT

The system and method for monitoring wear of one or more aircraft parts, such as an aircraft brake, an aircraft tire, a standby system, and landing gear. One or more sensors are provided for sensing a parameter of usage, and an estimate of usage of the part can be determined based upon the signal indicating the sensed value of the parameter of usage of the aircraft part. A plurality of sensors can be provided for sensing usage of a plurality of parts of the aircraft, and the estimate of usage of the part can be stored for access of the estimate by ground personnel. As applied to monitoring wear of an aircraft brake, a linear brake wear indicator attached to the brake moves a discrete distance when the brake is actuated, and a linear position encoder measures the distance travelled by the linear brake wear indicator as an indication of brake usage. A wheel speed monitor may also be provided for measuring the aircraft wheel speed, for distinguishing between static brake applications and moving brake applications, based upon the wheel speed signal.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a divisional of Ser. No. 11/127,666, filed May 11, 2005, whichis a continuation of Ser. No. 10/689,786, filed Oct. 20, 2003, now U.S.Pat. No. 6,929,333, which is a continuation of Ser. No. 10/008,607,filed Dec. 4, 2001, now U.S. Pat. No. 6,659,233. Each of theseapplications is hereby incorporated herein by reference as if set forthin full herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to monitoring of usage of aircraftparts, systems and functions, and more particularly concerns monitoringof aircraft braking systems.

2. Description of Related Art

Automatic braking systems have been commonly provided on commercialaircraft to aid the deceleration of the aircraft upon landing. As thesize and complexity of aircraft have increased, the automatic brakingsystems have also become more complex and computerized. Modern anti-skidsystems incorporated into aircraft braking systems commonly optimizebraking efficiency by adapting to runway conditions and other factorswhich affect braking in order to optimize deceleration, typicallycorresponding to the level of brake pressure selected by the pilot.

In a conventional skid detection system used in aircraft braking systemstypically includes a wheel speed transducer for each wheel brake of thewheels of the aircraft, for measuring wheel speed and generating wheelspeed signals that are a function of the rotational speed of the brakewheel. The wheel speed signal is typically converted to a signalrepresenting the velocity of the aircraft, and compared with a desiredreference velocity, to generate wheel velocity error signals indicativeof the difference between the wheel velocity signals from each brakedwheel and the reference velocity signal for providing anti-skid controlof aircraft braking.

Aircraft brakes often constitute the most expensive single maintenanceitem to the airlines, because they wear out and are expensive toreplace. The demands on aircraft brakes are extraordinary due to thehigh speeds at which aircraft braking typically occurs, causing aircraftbrakes to periodically wear out and require replacement. In emergencybraking situations, reverse thrust may not be available, highperformance engines can take several seconds to reduce thrust, andflight control surfaces may be able to generate little aerodynamic drag,placing the burden of slowing the aircraft almost completely on theaircraft braking system. In such situations, although the aircraft wheelsize may be comparable to that of an average car, the amount of energythat must be absorbed per brake can be equivalent to what a car brakewould absorb completely stopping an average car from a speed of 60 milesan hour 200 times.

Aircraft brakes are typically have a brake stack formed of multipledisks, in which the key elements are the rotors and stators which absorbthe energy of a stop. The rotors are keyed to and rotate along with thewheels, while the stators, tied to the axle, are stationary.Hydraulically operated brake pistons compress the rotors and statorstogether to provide the frictional forces necessary to brake anaircraft. One or more metal wear pins are attached to the pressureplate, or first stator, of a brake stack, and extend through a hole inthe brake's actuator housing. When the brake is new, the pins extendpast the housing by some amount (e.g. one or two inches). As the brakewears, the pressure plate moves away from the brake actuator housing,and the wear pins move with the pressure plates. The stroke of the brakepistons is automatically adjusted by brake actuator adjusters based uponthe brake wear indicated by the wear pins, so that when the brakes arereleased, the actuators only retract a fixed small amount, independentof brake wear.

Aircraft brakes are commonly guaranteed for a given number of landings,and the number of landings is commonly used as the overall measure ofbrake usage. However, the rate at which aircraft brakes wear and requirereplacement, and hence the cost of maintenance of aircraft brakes, isheavily dependent upon how such aircraft brakes are used. Factors suchas aircraft wheel speed and brake pressure, as well as how an operatorapplies brakes during each flight cycle can greatly affect aircraftbrake wear. There thus remains a need for an improvement in themonitoring of aircraft brake usage. Improved aircraft brake usagemonitoring would provide a better basis for guaranteeing brakes, andwould provide valuable data to help the airline operator improve landingand braking procedures to achieve lower brake costs. The presentinvention meets these needs.

SUMMARY OF THE INVENTION

Briefly, and in general terms, the present invention provides for asystem and method for monitoring aircraft braking system usage that canreduce aircraft operating costs by providing data which may be used tobetter guide operating and maintenance procedures. The present inventionprovides for continuous monitoring of brake wear, and stores one or morekey parameters affecting brake wear for periodic access by groundpersonnel. The brake usage data will provide a more accurate basis forguaranteeing the life of aircraft brakes, determining when aircraftbrakes need to be replaced, and will provide data for improving pilotlanding and braking techniques to achieve better brake economics.

The present invention accordingly provides for a system and method formonitoring wear of one or more aircraft parts. In a presently preferredembodiment, an aircraft brake is monitored for wear, although theinvention can also apply to monitoring of wear of other aircraft parts,such as an aircraft tire, a standby system, landing gear, and the like.In the system and method of the invention, one or more sensors areprovided for sensing a parameter of usage of the one or more aircraftparts and for generating a signal indicating a sensed value of theparameter of usage of the aircraft part. An estimate of usage of thepart is determined based upon the signal indicating the sensed value ofthe parameter of usage of the aircraft part. In one preferred aspect,the estimate of usage of the part is stored for access of the estimateby ground personnel. In another preferred aspect, the one or moresensors for sensing a parameter comprises a plurality of sensors forsensing usage of a plurality of parts of the aircraft, and the means fordetermining an estimate of usage comprises a central computer.

In a presently preferred embodiment, an aircraft brake is monitored forwear, and the one or more sensors comprise a linear brake wear indicatorattached to the brake. Each time the brake is actuated, the linear brakewear indicator moves a discrete distance, and a linear position encoderis provided for measuring and generating a linear position signalindicating the distance travelled by the linear brake wear indicator asan indication of brake usage. An estimate of brake usage is determinedbased upon the distance travelled by the linear brake wear indicator asindicated by linear position signal.

In one presently preferred embodiment, as applied to monitoring wear ofan aircraft brake, a wheel speed monitor is provided for generating awheel speed signal indicating wheel speed of the aircraft, and the meansfor determining an estimate of usage receives the wheel speed signal fordistinguishing between static brake applications and moving brakeapplications, based upon the wheel speed signal. In another currentlypreferred aspect, means are provided for measuring the period of timeelapsed during each brake application, and the distance over which eachbrake application occurs is determined based upon the wheel speed duringeach brake application and the period of time elapsed during each brakeapplication, in order to determine the degree to which each individualbrake application contributes to brake wear.

In another currently preferred embodiment, as applied to monitoring wearof an aircraft brake, a temperature sensor is provided for sensing braketemperature, and for generating a temperature signal indicating braketemperature that is received by the means for determining an estimate ofusage. The estimate of brake usage can be determined based upon theinput of the temperature signal. In another presently preferred aspect,the degree to which each individual brake application contributes towear can be estimated based upon the temperature signal.

In another presently preferred embodiment, as applied to monitoring wearof an aircraft tire, a wheel speed monitor is provided for generating awheel speed signal indicating wheel speed of the aircraft, and the wheelspeed signal can be used for distinguishing between static brakeapplications and moving brake applications based upon the wheel speedsignal, and for determining an estimate of tire usage. A sensor is alsopreferably provided for sensing aircraft yaw, and for generating a yawsignal indicating aircraft yaw, that can be used for determining anestimate of tire wear based upon the wheel speed signal and the yawsignal.

In another presently preferred embodiment, when the aircraft part to bemonitored is a standby system, a sensor is provided for sensing inputpower to the standby system and for generating an input power signalused for determining an estimate of usage. Means are also preferablyprovided for measuring the period of time elapsed during each usage ofthe standby system and for generating an elapsed time signal fordetermining an estimate of usage of the standby system based upon theinput power signal and the elapsed time signal.

In another presently preferred embodiment, when the aircraft part to bemonitored is a landing gear, a sensor is provided for sensing load onthe landing gear and for generating a load signal for determining anestimate of usage of the landing gear. Means are also preferablyprovided for measuring the period of time elapsed during each usage ofthe landing gear and for generating an elapsed time signal fordetermining an estimate of usage of the landing gear based upon the loadsignal and the elapsed time signal.

These and other aspects and advantages of the invention will becomeapparent from the following detailed description and the accompanyingdrawings, which illustrate by way of example the features of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram generally illustrating the system andmethod of the invention for monitoring wear of one or more aircraftparts;

FIG. 2 is a schematic diagram illustrating a preferred embodiment of thesystem and method of the invention for monitoring wear of an aircraftbrake;

FIG. 3 is a schematic diagram of a linear brake wear indicator andlinear position encoder of FIG. 2;

FIG. 4 is a schematic diagram illustrating a preferred embodiment of thesystem and method of the invention for monitoring wear of an aircrafttire;

FIG. 5 is a schematic diagram illustrating a preferred embodiment of thesystem and method of the invention for monitoring wear of an aircraftstandby system; and

FIG. 6 is a schematic diagram illustrating a preferred embodiment of thesystem and method of the invention for monitoring wear of an aircraftlanding gear.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While wear of aircraft brakes is commonly estimated by the number oflandings in which aircraft brakes are used, other factors affecting howaircraft brakes are used, including aircraft wheel speed and brakepressure, how an operator applies brakes during each flight cycle, andbrake temperature. Improved brake usage monitoring can also be combinedwith the monitoring of usage of other aircraft parts, to provide abetter basis for guaranteeing aircraft parts, and to provide valuabledata to help the airline operator improve landing and brakingprocedures, as well as other operating procedures, to achieve loweroperating costs.

As is illustrated in the drawings, the invention accordingly providesfor a system and method for monitoring wear of one or more aircraftparts. Referring to FIG. 1, a system 10 is provided for monitoring wearof one or more aircraft parts 12, utilizing one or more sensors 14 forsensing a parameter of usage of the one or more aircraft parts,respectively, and for generating signals 16 indicating a sensed value ofthe parameter of usage of the one or more aircraft parts, such as anaircraft brake, an aircraft tire, an aircraft standby system, anaircraft landing gear, and the like. In a presently preferred aspect, aplurality of sensors are provided for monitoring usage of a plurality ofparts of an aircraft. The invention also provides for a control means 18for determining an estimate of usage of the part based upon the signalindicating the sensed value of the parameter of usage of the aircraftpart, such as a central computer of an anti-skid control system as willbe further explained below, that receives the inputs of the one or moresensors. The control means for determining an estimate of usagepreferably also includes storage means such as a computer memory 20 forstoring the estimate of usage of the part, and means for accessing theinformation concerning the estimated part usage, such as one or moreports or terminals 22 providing access by ground equipment andpersonnel, for example.

In a presently preferred embodiment illustrated schematically in FIG. 2,the aircraft part for which usage is to be monitored is an aircraftbrake 24, typically having a plurality of rotors 26 and stators 28 whichabsorb the energy of a stop. The rotors are keyed to and rotate alongwith the wheel (not shown), while the stators, tied to the axle (notshown), are stationary. In some brake designs, a light spring (notshown) may also be added to the wear pin to assure that the first statorof the brake remains in contact with the brake actuator at all times.Hydraulically operated brake pistons 30 compress the rotors and statorstogether to provide the frictional forces necessary to brake anaircraft. One or more linear brake wear indicators 32, such as metalwear pins, for example, are attached to the pressure plate 34, the firststator of the brake stack, and extend through a hole in the brake'sactuator housing 38.

Each linear brake wear indicator extends to an associated linearposition encoder 40 for measuring linear position of the correspondinglinear brake wear indicator, which generates a linear position signal 42indicating the linear position of the linear brake wear indicator andthereby the distance travelled by the linear brake wear indicator, sinceeach time the brake is actuated, the linear brake wear indicator moves adiscrete distance as the piston moves from its “Brakes Off” position toits “Brakes On” position that thus can be measured by observing maximumand minimum readings of the linear position sensor. This discrete amountremains relatively constant, independent of brake wear, as is providedfor by the “Adjusters” typically present in brakes. The linear positionsignal is received by the control means, for determining an estimate ofdistance travelled by the linear brake wear indicator when the brake isactuated, as an indication of brake usage, and for determining anestimate of usage of the brake based upon the linear position signal.

As is illustrated in FIG. 3, in a presently preferred embodiment, thelinear brake wear indicator includes a plurality of longitudinallyarranged markings 44 and the linear position encoder comprises anoptical encoder 46 for counting the markings passing by the opticalencoder for determining the distance traveled by the linear brake wearindicator upon brake actuation, for indicating the distance travelled bythe linear brake wear indicator as an indication of brake usage. In analternate embodiment, the markings on the linear brake wear indicatormay include a plurality of longitudinally arranged digitized markingsindicating longitudinal position on the linear brake wear indicator, andthe linear position encoder may comprise an optical encoder for encodingthe digitized markings, for indicating the distance travelled by thelinear brake wear indicator as an indication of brake usage. Thismeasure of brake applications can, on its own, provide a much superiormeasure of brake usage than a “number of landings” measure according tothe current method of estimating brake wear. However, this inventionprovides for additional data to be monitored to yield a better measureof brake usage.

Referring again to FIG. 2, when the aircraft part for which usage is tobe monitored is an aircraft brake, the system and method of theinvention also utilizes a wheel speed monitor 50 for generating a wheelspeed signal 52 indicating wheel speed of the aircraft. In one presentlypreferred aspect, the wheel speed monitor comprises a wheel speedsensor, and the control means receives the wheel speed signal fordistinguishing between static brake applications and moving brakeapplications based upon the wheel speed signal. In an alternatepreferred embodiment, the wheel speed monitor comprises an aircraftspeed sensor, which can also be used for determining the wheel speed ofthe aircraft. As is illustrated in FIG. 2, the control means alsopreferably includes clock means 54 for measuring the period of timeelapsed during each brake application, and means for determining thedistance over which each brake application occurs, based upon the wheelspeed during each brake application and the period of time elapsedduring each brake application, for determining the degree to which eachindividual brake application contributes to brake wear.

Again with reference to FIG. 2, in another presently preferred aspect,when the aircraft part for which usage is to be monitored is an aircraftbrake, the system and method of the invention optionally also utilizes abrake temperature sensor 56 for generating a brake temperature signal 58that is received by the control means for determining an estimate ofusage based upon the temperature signal. The control means preferablyincludes means for estimating the degree to which each individual brakeapplication contributes to wear based upon the temperature signal.

In another presently preferred embodiment, illustrated in FIG. 4, thesystem and method of the invention can optionally monitor the usage andwear of an aircraft tire 60. Sensors that can be provided for sensingparameters of usage of an aircraft tire include the wheel speed monitor,as described above, and means 62 for sensing aircraft yaw, which is theside to side, turning about a vertical axis, such as by an inertialguidance system, such as the type using three gyroscopes and threeaccelerometers for determining a vehicle's roll, pitch, and yaw motion.The means for sensing aircraft yaw generates a yaw signal 64 indicatingaircraft yaw, that is received as an input by the control means fordetermining an estimate of tire usage and wear, based upon the wheelspeed signal and the yaw signal.

In another presently preferred embodiment, illustrated in FIG. 5, thesystem and method of the invention can optionally monitor the usage andwear of a standby system 66. Sensors that can be provided for sensingparameters of usage of a standby system include means 68 for sensinginput power, such as a watt-hour meter for measuring the electric powerflowing through a circuit to the standby system over time, whichgenerates an input power signal 70 received as an input by the controlmeans, for determining an estimate of usage of the standby system, basedupon the standby system power signal, and an elapsed time signal fromthe system clock, as described above.

In another presently preferred embodiment, illustrated in FIG. 6, thesystem and method of the invention can optionally monitor the usage andwear of an aircraft landing gear 72. Sensors that can be provided forsensing parameters of usage of an aircraft landing gear include means 74for sensing load on the landing gear, such as one or more strain gaugesor other type of strain sensors strategically placed on the landinggear, for example, and for generating a load signal 76 received as aninput by the control means for determining an estimate of usage and wearof the aircraft landing gear, based upon the load signal and an elapsedtime signal from the system clock, as described above.

As described above, the present invention provides for the gathering ofthe brake usage data, and optionally other part usage data, into acomputer, where the part usage data is operated on to estimate brakewear and optionally other part wear, stored, and can be later accessedby ground personnel. Although there are numerous existing technologiesfor doing this, the embodiment illustrated and described uses theanti-skid system, since the anti-skid system already contains a wheelspeed monitor and computer and, as such, is a convenient place. Theexact algorithms used to estimate brake usage will vary with the exactbrake or other part in question, and the degree of accuracy desired(e.g. brake temperature may not be included). In a presently preferredembodiment, the functions of the elements in the control means,including the clock means, means for determining distance, means forestimating the degree to which each individual brake applicationcontributes to wear based upon brake temperature, for determining yawand tire wear based upon yaw, for determining wear of a standby system,and for determining wear of an aircraft landing gear, are performed byone or more microprocessors under appropriate software control, althoughalternatively these or analogous functions may be performed by suitablehardware components.

It will be apparent from the foregoing that while particular forms ofthe invention have been illustrated and described, various modificationscan be made without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the invention belimited, except as by the appended claims.

1. A system for monitoring wear of an aircraft brake, comprising: meansfor measuring a period of time elapsed during each brake application; awheel speed monitor for generating a wheel speed signal indicating wheelspeed of the aircraft; means for distinguishing between static brakeapplications and moving brake applications based upon said wheel speedsignal; and means for determining an estimate of usage of said brake andfor determining the degree to which each individual brake applicationcontributes to brake wear, said means for determining an estimate ofusage receiving said wheel speed signal and determining a distance overwhich each brake application occurs based upon the wheel speed of theaircraft during each brake application and said period of time elapsedduring each brake application.
 2. The system of claim 1, furthercomprising at least one sensor for sensing input power to a standbysystem and for generating an input power signal; and means for measuringthe period of time elapsed during each usage of said standby system andfor generating an elapsed time signal received by said means for meansfor determining an estimate of usage, and said means for determining anestimate of usage receiving said input power signal for determiningusage of said standby system based upon said input power signal and saidelapsed time signal.